Treatment Of Refractory Organic Pollutants Research Articles

Efficient tetracycline degradation via flow-through peroxymonosulfate activation by dual heteroatom-doped wood-derived catalytic membrane

The widespread use of antibiotics in the medical industry and in animal husbandry has led to significant environmental pollution. Effective purification of high concentrations of tetracycline (TC) in practical pharmaceutical wastewater remains a substantial challenge. The integration of advanced oxidation with membrane separation technology shows great application potential. In this study, a P and N co-doped balsa wood membrane (PNWM) were fabricated using heteroatomic doped biochar material, aiming to synergize filtration and catalytic oxidation. The catalytic activity of the PNWM/peroxymonosulfate (PMS) system was systematically evaluated. Targeting TC as the pollutant, the PNWM/PMS system achieved a degradation efficiency exceeding 97 % within 30 min and a total organic carbon (TOC) removal efficiency of 63.9 %, surpassing the performance of unmodified wood-based membrane. These excellent results were attributed to the doping of N and P atoms, which increased surface defects and specific area, thereby enhancing the adsorption and degradation of TC by PNWM. The graphite N facilitated electron transfer, while pyridine N served as active sites for PMS activation. Additionally, the low electronegativity of the P formed electronic regions of varying intensities on the PNWM surface, contributing to PMS activation. The membrane process also enhanced mass transfer during the degradation process. Both radical (·OH, SO4·ˉ, O2·ˉ) and non-radical (1O2, electron transfer) pathways cooperated in TC degradation in PNWM/PMS system. Consequently, heteroatom-doped biochar film materials prepared through simple methods provide a promising approach for the effective treatment of refractory organic pollutants in wastewater.

Enhanced Photocatalytic Ozonation Using Modified TiO2 With Designed Nucleophilic and Electrophilic Sites.

Photocatalytic ozonation is considered to be a promising approach for the treatment of refractory organic pollutants, but the design of efficient catalyst remains a challenge. Surface modification provides a potential strategy to improve the activity of photocatalytic ozonation. In this work, density functional theory (DFT) calculations were first performed to check the interaction between O3 and TiO2-OH (surface hydroxylated TiO2) or TiO2-F (surface fluorinated TiO2), and the results suggest that TiO2-OH displays better O3 adsorption and activation than does TiO2-F, which is confirmed by experimental results. The surface hydroxyl groups greatly promote the O3 activation, which is beneficial for the generation of reactive oxygen species (ROS). Importantly, TiO2-OH displays better performance towards pollutants (such as berberine hydrochloride) removal than does TiO2-F and most reported ozonation photocatalysts. The total organic carbon (TOC) removal efficiency reaches 84.4 % within two hours. This work highlights the effect of surface hydroxylation on photocatalytic ozonation and provides ideas for the design of efficient photocatalytic ozonation catalysts.

Efficient hydrogen peroxide synthesis with Pluggable Capsule cathode for Electro-Fenton treating actual landfill leachate

Membrane concentrate of landfill leachate is the typical refractory wastewater with high contaminants concentration, high complexity, and high toxicity, posing a huge potential threat to the surface and subsurface water. Electro-Fenton (EF) based on in-situ synthesis of H2O2 is an effective method for the treatment of refractory organic pollutants. However, the low accumulative concentration of H2O2 and the poor scalability of the system remain major bottlenecks, limiting the practical application of EF. This study presented a modular air-breathing cathode, Pluggable Capsule Cathode (PCC), for efficient in-situ H2O2 synthesis through 2-electron oxygen reduction reaction (ORR). Based on PCC, corridor reactors (CR) were fabricated for in-situ H2O2 synthesis and actual landfill leachate treatment. Operated under the optimal conditions (dual-chamber, A/V=240 cm2 L−1, 2 M NaOH electrolytes and J=20 mA cm−2), the H2O2 concentration reached 28.1 g/L. In the EF system based on single-chamber CR equipped with PCCs, 81 % of COD and 89 % of NH3-N in landfill leachate were removed within 3 h. The total cost of landfill leachate treatment by the EF system based on CR-PCC was calculated as $ 5.06 m−3. The PCC based EF system was a promising process for the treatment of actual refractory wastewater, which provides a new insight for the structure design of cathode and reactor in the future.

Nitrogen-doped carbon-coated Cu0 activates molecular oxygen for norfloxacin degradation over a wide pH range

The Fenton-like activated molecular oxygen technology demonstrates significant potential in the treatment of refractory organic pollutants in wastewater, offering promising development prospects. We prepared a N-doped C-coated copper-based catalyst Cu0/NC3-600 through the pyrolysis of Mel-modified Cu-based metal–organic framework (MOF). The results indicate that the degradation of 20 mg/L norfloxacin (NOR) was achieved using 1.0 g/L Cu0/NC3-600 across a wide pH range, with a removal rate exceeding 95 % and total organic carbon (TOC) removals approaching 70 % after 60 min at pH 5–11. The nitrogen doping enhances the electronic structure of the carbon material, facilitating the adsorption of molecular oxygen. Additionally, the formed carbon layer effectively prevent copper leaching,contributing to increased stability to a certain extent. Subsequently, we propose the catalytic reaction mechanism for the Cu0/NC/air system. Under acidic conditions, Cu0/NC3-600 activates molecular oxygen to produce the •O2–, which serves as the primary active species for NOR degradation. While in alkaline conditions, the high-valent copper species Cu3+ is generated in conjunction with •O2–, both working simultaneously for NOR degradation. Furthermore, based on the LC-MS results, we deduced four possible degradation pathways. This work offers a novel perspective on expanding the pH range of copper-based catalysts with excellent ability to activate molecular oxygen for environmental water treatment.

Construction of ZnFe2O4/g-C3N4 nanocomposite catalyst for degradation of organic compound through photodegradation and heterogeneous Fenton oxidation

ZnFe2O4/g-C3N4 heterojunction nanocomposite photocatalyst was prepared by one-step solvothermal method using graphite carbon nitride (g-C3N4) and zinc ferrate (ZnFe2O4), and characterized by SEM/EDX, XRD, FT-IR, Zeta potential, and VSM. The cationic-dye methylene blue (MB) was selected as the target pollutant for photocatalytic degradation and the degradation mechanism of the heterogeneous nanocomposite photocatalyst was analyzed. The photocatalyst can accelerate the separation of photogenerated electron-hole pairs, increase the number of photocatalytic reaction sites, and have strong REDOX ability and charge transport ability. The degradation efficiency of MB is 3 times and 2 times of that of pure g-C3N4 and ZnFe2O4, respectively. Visible light (Vis)/ZnFe2O4/g-C3N4/sodium percarbonate (SPC) photo-Fenton system established under the synergistic effect of ZnFe2O4/g-C3N4 and SPC can continuously produce ·OH, ·O2− and h+. In half an hour, 93% of MB was degraded by Vis/ZnFe2O4/g-C3N4/SPC, and the degradation rate of MB was above 90% for 5 consecutive cycles. Through characterization and water treatment experiments, ZnFe2O4/g-C3N4 heterostructure nanocomposite photocatalyst has the characteristics of high efficiency photocatalytic oxidation activity, stability, superparamagnetism, easy separability and reusability, and can be reused continuously. Therefore, it is a promising photocatalyst in the field of wastewater treatment and a potential candidate material for the treatment of refractory organic pollutants.

Synergistic enhancement of redox pairs and functional groups for the removal of phenolic organic pollutants by activated PMS using silica-composited biochar: Mechanism and environmental toxicity assessment

In present work, a novel catalyst of cobalt supported on silica-composited biochar (Co@ACFA-BC) derived from fly ash and agricultural waste was synthesized. A series of characterizations confirmed that Co3O4 and Al/Si–O compounds were successfully embedded on the surface of biochar, which triggered superior catalytic activity for PMS activation towards phenol degradation. Particularly, the Co@ACFA-BC/PMS system could completely degrade phenol in the wide pH range, and was almost unaffected by environmental factors including humic acid (HA), H2PO4−, HCO3−, Cl−, and NO3−. Further quenching experiment and EPR analysis proved that both radical (SO4·-, ·OH, O2·-) and non-radical (1O2) pathways were involved in the catalytic reaction system, and the excellent PMS activation was attributed to the electron pair cycling of Co2+/Co3+ and the active sites provided by Si–O–O and Si/Al–O bonds on the catalyst surface. Meanwhile, the carbon shell effectively inhibited the leaching of metal ions, enabling the Co@ACFA-BC catalyst to maintain excellent catalytic activity after four cycles. Finally, biological acute toxicity assay demonstrated that the toxicity of phenol could be significantly reduced after being treated by Co@ACFA-BC/PMS. Overall, this work provides a promising strategy for solid waste valorization and a feasible methodology for green and efficient treatment of refractory organic pollutants in water environment.

Confining Fe2O3 in Silicalite-1 for effective catalytic activity in bias-assisted photo-Fenton system for nitrobenzene degradation

Removal of refractory organic pollutants by photo-Fenton process is of great significance to cleaner production. Low yield and utilization of photogenerated carriers limit the application of photo-Fenton process. Positive bias voltage is introduced into the photo-Fenton system for the first time so that the photogenerated electrons no longer flow to the external circuit but participate in the redox cycle of the photo-Fenton reaction. Under the applied bias voltage of +0.3 V, the efficiency of the system to degrade nitrobenzene reaches 95.4% in 60 min and still has 90.3% of nitrobenzene degradation efficiency after five runs while the photo-Fenton system without bias voltage is 80.0%. The bias voltage makes the band bending so that the band gap narrow, leading to easier generation of photogenerated electrons. Then the separated photogenerated electrons combine with Fe3+, which promotes the rapid redox cycle of Fe3+/Fe2+ in the photo-Fenton reaction. Both photogenerated electrons and holes are efficiently utilized in this work, which provides a new method for chemical treatment of refractory organic pollutants.

Mechanism and efficiency research of P- and N-codoped graphene for enhanced paracetamol electrocatalytic degradation.

Electrocatalytic oxidation is an effective technology for treatment of refractory organic pollutants, and its performance strongly depends on anode materials. Among all anode materials, graphene (GN) owns the advantages of high stability and lack of secondary pollution. The catalytic performance of GN can be further improved through heteroatom doping. Here, P/N-codoped graphene (PN-GN) materials were optimized and used as an anode material for 4-acetamidophenol (APAP) electrocatalytic degradation. Result indicated that PN-GN had lower internal resistance, larger specific surface area, and higher electrochemical activity than single-doped graphene materials. The catalytic activity of GN was greatly improved by P/N codoping. When PN-GN (P8.4%-N7.6%-500°C) was used as catalyst (current of 20mA, initial pH of 7, reaction time of 60min), the degradation efficiency of APAP reached 98.2% ± 1.8%, which was 17.9% ± 3.6% higher than P-codoped graphene (P-GN), 14.7% ± 4.6% higher than N-codoped graphene (N-GN), and 54.0% ± 5.2% higher than GN. After 180min of reaction, the degradation efficiency of total organic carbon (TOC) was 78.5%. The reaction conditions were optimized and the degradation pathway of APAP was estimated to elucidate the catalytic mechanism. The main active substances generated in the system were identified as active chlorine and O2•-.

Enhanced Electro-Fenton Degradation of Ciprofloxacin by Membrane Aeration

Electro-Fenton is a widely used electrochemical advanced oxidation process for the treatment of refractory organic pollutants, in which O2 input is required to generate hydrogen peroxide. The aeration mode directly affects the dissolution and stability of O2 bubbles in the solution, thus the rate of degradation. Herein, membrane aeration was introduced to the electro-Fenton degradation of ciprofloxacin in which O2 was dispersed into the liquid phase in the form of microbubbles through the ceramic membrane. Microbubbles can greatly improve the gas–liquid mass transfer efficiency of unit volume O2 to obtain an ultrahigh concentration of dissolved O2 up to 46 mg/L, thus improving the reaction rate. The effects of aeration mode, applied current, membrane aperture, aeration rate, and ciprofloxacin concentration on degradation rate were studied. Compared with the conventional electro-Fenton process using plastic pipe aeration, the membrane aeration-enhanced electro-Fenton (MAEF) system achieved a significant improvement in the degradation rate, and the reaction time required to achieve a 97% degradation ratio was remarkably reduced from 4 h to 10 min. Membrane aeration is an efficient approach to facilitating heterogeneous catalysis reactions involving the gas phase.

(Fe0.67Mn0.33)OOH riched in oxygen vacancies facilitated the PMS activation of modified EMR for refractory foaming agent removal from mineral processing wastewater

A novel ternary composite catalyst (FeOOH/Fe2O3/(Fe0.67Mn0.33)OOH) directly prepared from electrolytic manganese residue was applied for terpineol degradation in this study. The reaction system could remove 76.8% of chemical oxygen demand (COD) from simulated water containing terpineol (100 mg/L), while the degradation process could be accelerated under alkaline condition (84.6% at pH 9.0). The degradation performances of Fe2O3, FeOOH and (Fe0.67Mn0.33)OOH indicated that the in-situ formed (Fe0.67Mn0.33)OOH riched in oxygen vacancies (OV) could promote the PMS activation activity of catalyst mainly ascribed by enhancing interfacial electron transfer. The ·OH was the primary active radical, the production of which was favored by the metal−OH. This ternary composite catalyst had anti-jamming ability toward most common ions. Further, this system also displayed an outstanding degradation ability for actual mineral processing wastewater (93.2% COD removal). The developed system expanded the horizon for the high-value utilization of metallurgical slag and the treatment of refractory organic pollutants in mineral processing wastewater.

Synergistic effect of underwater arc discharge plasma and Fe2O3-CoFe2O4 enhanced PMS activation to efficiently degrade refractory organic pollutants

This study employed a self-designed underwater arc discharge (UAD) plasma reactor, which combined advanced oxidation process (Fe2O3-CoFe2O4/PMS) and low-temperature plasma technology to efficiently degrade refractory organic pollutants (i.e. phenol, p-chlorophenol, p-nitrochlorobenzene). The results illustrated that the plasma/PMS/Fe2O3-CoFe2O4 system possessed high degradation efficiency and TOC removal rate towards three target pollutants (phenol: 99.8%, 96.12%; 4-CP: 98.4%, 86.48%; p-NCB: 99.9%, 88.31%). With the help of in-situ variable temperature EPR and Indigo colorimetry method, ·OH, SO4·-, O2·-, 1O2 and O3 were identified as the main reactive oxygen species (ROS) for the degradation of target pollutants, revealing the synergistic catalytic mechanism between plasma and Fe2O3-CoFe2O4 for PMS activation and inferring the degradation pathways of target pollutants. The results confirmed that the plasma/PMS/Fe2O3-CoFe2O4 system was feasible for the degradation of refractory organic pollutants, has the advantages of high efficiency and low energy consumption, and could provide an effective strategy for the treatment of refractory organic pollutants in groundwater/soil.

Flow-through heterogeneous electro-Fenton based on Co-CNT/Ti3C2TX membrane for improved tetracycline removal in wide pH ranges

The heterogeneous electro-Fenton (HEF) membrane has shown great potential for the treatment of refractory organic pollutants, but its degradation efficiency and applicability for addressing practical organic pollutant issues needs to be improved.

Highly efficient photosynthesis of hydrogen peroxide in ambient conditions

Photosynthesis of hydrogen peroxide (H2O2) in ambient conditions remains neither cost effective nor environmentally friendly enough because of the rapid charge recombination. Here, a photocatalytic rate of as high as 114 μmol⋅g-1⋅h-1 for the production of H2O2 in pure water and open air is achieved by using a Z-scheme heterojunction, which outperforms almost all reported photocatalysts under the same conditions. An extensive study at the atomic level demonstrates that Z-scheme electron transfer is realized by improving the photoresponse of the oxidation semiconductor under visible light, when the difference between the Fermi levels of the two constituent semiconductors is not sufficiently large. Moreover, it is verified that a type II electron transfer pathway can be converted to the desired Z-scheme pathway by tuning the excitation wavelengths. This study demonstrates a feasible strategy for developing efficient Z-scheme photocatalysts by regulating photoresponses.

Efficient degradation of Congo red and phenol by a new photocatalyst Ag/AgBr-Al-attapulgite composite under visible light irradiation.

Nowadays the concern on the treatment of refractory organic pollutants (e.g., Congo red and phenolic compounds) in industrial wastewaters and their treated effluents with conventional technologies has been still continuously increasing. In this study, a novel visible light photocatalyst material, Ag/AgBr and Al loading on the attapulgite (ATP), was prepared for efficiently catalyzing the photodegradation of the two refractory substances, and its photocatalytic performance and recyclability were assessed. Results from transmission electron microscopy and X-ray diffraction confirmed the successful loading of Ag/AgBr and Al on the ATP. The prepared Ag/AgBr-Al-ATP composite presented substantially better catalytic performance than Ag/AgBr alone probably because the ATP as a carrier of catalyst provided more contact surface for catalyst Ag/AgBr and Congo red/phenol. In the Ag/AgBr-Al-ATP composite, the photocatalyst AgBr content increased from 20.4 to 34.9% due to the modification of ATP by Al. Correspondingly, the Ag/AgBr-Al-ATP composite presented its excellent photocatalytic performance under visible light irradiation: photodegradation efficiencies of Congo red and phenol of 1.73 mg/100 mg and 0.86 mg/100 mg were achieved. With the increase of pH, the photolysis efficiencies of Congo red and phenol both first increased and then decreased, whereas the optimal photocatalytic performance occurred at pH 7 for Congo red and pH 10 for phenol. The Ag/AgBr-Al composite presented a high catalytic activity for photolysis of Congo red and phenol in all the four consecutive reused cycles. The results in this study comprehensively demonstrated a promising photocatalyst for efficient removal of the similar refractory organics presented in industrial wastewaters, which deserves further investigation and development.

Flower-like MoS2/BiFeO3 doped silver orthophosphate catalyst for visible-light assisted treatment of refractory organic pollutants

The development of MoS2/BiFeO3 embedded silver orthophosphate ternary composite for the excellent photocatalytic abatement of refractory pollutants was established. The fabrication of a confounded heterojunction photocatalyst composite for the enhanced treatment of various dyes, pesticides and antibiotic drugs with extra stability and observable reproducibility are possible. The acid dye methyl orange, basic dyes such as methylene blue, rhodamine B and an azo dye acid red 18 were successfully degraded with above 90% degradation efficiency within a very short time period. These results highlighted that the degradation efficiency of the developed composite was 8 times higher than the pure Ag3PO4 catalyst. Also, the hazardous herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) was degraded and mineralized within 180 min, the most toxic insecticide acephate was degraded within 60 min and the antibiotic tetracycline was removed in 120 min with accountable mineralization. All the pesticides and antibiotic formed less toxic degraded products and the products were corroborated with high resolution mass spectrum (HRMS). The radical scavenger experiment reveals that the active species for photodegradation study was photogenerated holes. These are produced by the rapid transfer of electrons through Ag3PO4 due to its low recombination tendency. In short, the development of Ag3PO4 based ternary composite for the better visible light assisted catalytic degradation of refractory pollutants such as dyes, pesticides and pharmaceutical drugs were carried out with excellent efficiency.

Enhanced synergistic performance of nano-Fe0-CeO2 composites for the degradation of diclofenac in DBD plasma

Dielectric barrier discharge (DBD) is an attractive advanced oxidation process (AOP) due to its operational convenience and environmental friendliness. However, DBD plasma suffers from relatively low energy utilization, which limits its commercial application. In this study, nano-Fe0-CeO2 is successfully synthesized and used for DBD plasma degradation of diclofenac (DCF). The results show that the nano-Fe0-CeO2 significantly enhances the removal of DCF. A DBD-Fe0-CeO2 system degrades 96.4% DCF within 10 min, which is higher than the DBD system alone (45.8%). The synergistic factor of the DBD system and nano-Fe0-CeO2 reaches 3.731. In addition, the composite catalyst shows ideal reusability. Substance activity and production experiments show that reactive oxygen species (ROS), especially OH, play a key role in the degradation of DCF. Nano-Fe0-CeO2 has synergistic effects with O3 and H2O2 and significantly promotes the generation of ROS in the DBD system. Based on the intermediates detected by liquid chromatography-mass spectrometry, a reasonable degradation pathway of DCF is proposed. Our findings are helpful for understanding the mechanism of DCF degradation by coupling nano-zero-valent-iron-based nanocomposites in a DBD system; they also provide an effective system for the treatment of refractory organic pollutants in water.

Degradation of methylene blue by intimate coupling photocatalysis and biodegradation with bagasse cellulose composite carrier

A novel highly efficient technology, intimate coupling photocatalysis and biodegradation (ICPB) for the treatment of refractory organic pollutants was introduced, and the carrier in ICPB based on sugarcane bagasse cellulose (SBC) was prepared. The SBC–TiO2 carrier produced was characterized using spectroscopy, microscopy, and diffraction techniques. The SEM image showed a rough and porous structure of the carrier, while as the EDS, XPS and XRD indicated that TiO2 was successfully added into the carrier, which retained its original crystal structure and provided the photocatalytic activity. The combined process of photocatalysis and biodegradation was much more efficient than a single process alone. The success in preparing bagasse cellulose based carrier in this study provided a significant contribution towards the development of a green and efficient technology system for the treatment of refractory organic matter.

Electrochemical treatment of organic pollutants in landfill leachate using a three-dimensional electrode system

The use of three-dimensional electrode is a new electrochemical oxidation technology for landfill leachate treatment. In this study, a particle electrode was developed using Fe/C granules, which were suspended between the cathode and the anode to create a three-dimensional electrode. The three-dimensional electrode activated sodium persulfate to treat landfill leachate. Fe/C granules were prepared by incorporating iron filings and hydrothermally carbonized biochar into alginate beads. The optimal parameters of the three-dimensional electrode for chemical oxygen demand (COD) removal from landfill leachate were determined based on a series of single factor experiments as an operating voltage of 5V, a sodium persulfate concentration of 28mM, and 1g of Fe/C granules. Treatment with the three-dimensional electrode at optimized conditions achieved 72.9% removal of COD and 99.9% removal of ammonia nitrogen, resulting in landfill leachate being clear and transparent. The changes in total organic carbon, nitrite, and nitrate concentrations indicated that most organic pollution and ammonia nitrogen were converted into CO2 and N2. This study provides an alternative technology for the treatment of refractory organic pollutants.

Insights into removal of tetracycline by persulfate activation with peanut shell biochar coupled with amorphous Cu-doped FeOOH composite in aqueous solution

Peanut shell biochar (BC) supported on Cu-doped FeOOH composite (Cu-FeOOH/BC) was synthesized using a facile and scalable method. The Cu-FeOOH/BC samples were characterized by Fourier transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), scanning electron microscopy equipped with an energy-dispersive spectrometer (SEM-EDS), x-ray photoelectron spectroscopy (XPS), and Brunauer-Emmett-Teller (BET) techniques. Novel catalytic composites with different Cu/Fe molar ratios were compared systematically by activating persulfate (PS) for the tetracycline (TC) degradation. 0.5Cu-1FeOOH/BC (Cu/Fe molar ratio = 0.5:1) was confirmed as the optimum activation material and the removal of TC reached 98.0% after 120min by combining with 20mM PS at pH 7.0 and 25°C. The influencing factors including catalyst loading, PS dosage, water matrix species, and pH on the performance system of 0.5Cu-1FeOOH/BC-PS were investigated, respectively. Reaction rate constants (Kobs) on catalyst dosages (0.05, 0.10, 0.20, and 0.30gL-1) were 0.0072, 0.0101, 0.0244, and 0.0144min-1, and 0.0090, 0.0146, 0.0244, and 0.0178min-1 for the change of PS concentrations (5, 10, 20, and 30mM), which indicated that increasing the concentrations of catalyst and PS appropriately improved TC degradation, but excessive dosages inhibited the reaction process of TC removal. The TC removal rate was inhibited by inorganic anions with the following order of HCO3- > Cl- > HPO42- > SO42- > NO3-. Free radical quenching and capture experiments under different pH values revealed that sulfate radicals existed predominantly in acidic conditions and hydroxyl radicals in alkaline conditions. The catalyst showed an excellent recyclability and stability and the removal efficiency of TC still remained over 90% after five consecutive uses. To conclude, coupling of 0.5Cu-1FeOOH/BC and PS can be successfully applied as an effective and stable technique for the treatment of refractory organic pollutants in wastewater.

Sustainable Strategy for Enhancing Anaerobic Digestion of Waste Activated Sludge: Driving Dissimilatory Iron Reduction with Fenton Sludge

Fenton process has been extensively applied for treatment of refractory organic pollutants. While the potentially hazardous iron-containing sludge generated from the Fenton process requires proper treatment and disposal, due to its high Fe contents and toxic organic matters involved. Considering that Fe(III) oxides exhibits an ideal potential for enhancing anaerobic digestion (AD), in this study Fenton sludge with a high-abundance of Fe(III) was introduced in AD of wasted activated sludge (WAS) with the aims to improve the sludge digestion as well as to remove the organic matters in Fenton sludge. Results showed that methane production and sludge reduction of WAS were significantly improved, and the organic matters contained in Fenton sludge was removed by 70.0%. Meanwhile, nearly a half of in Fenton sludge was converted to Fe2+ via dissimilatory iron reduction during the digestion, in agreement with microbial community analysis. The study suggests a Fe recycling between AD and Fenton process that Fenton ...